1. Field of the Invention
The invention relates to a hot-gas reciprocating machine having two or more working spaces, whose volumes can be varied at a mutual phase difference by piston-like bodies coupled to a crank shaft, a working medium which performs a thermodynamic cycle in each of the working spaces during operation, and a control device for supplying working medium; and more particularly to such a machine whose control device has a housing having an inlet which is connected to a source of pressurized working medium and a plurality of outlets, each of which outlets is separately connected to an associated working space. The housing accommodates a control member which, during each revolution of the crank shaft, successively brings each of the outlets separately into open communication with the inlet, each time for a period during which the maximum cycle pressure occurs in the interconnected working space.
Such a hot-gas reciprocating machine operating according to the Stirling cycle is known from the Netherlands patent application No. 7,407,951 laid open to public inspection, to which U.S. Pat. No. 4,045,978 corresponds.
In the context of the present invention, hot-gas reciprocating machines are to be understood to mean hot-gas reciprocating engines, cold-gas refrigerating machines and heat pumps. In each of the working spaces of these machines, the working medium is alternately compressed, when it is present mainly in a sub-space (the compression space) after which it is transported, through a regenerator, to another sub-space (the expansion space) subsequently, when the greater part of the working medium is present in the expansion space, it expands and is finally returned, through the regenerator, to the compression space, the cycle thus having been completed. The compression and the expansion space have mutually different mean temperatures during operation.
The piston-like bodies which vary the volumes of the various working spaces are coupled to the crank shaft at a different crank angle relative to each other.
As a result, a mutual phase difference exists between the working spaces as regards the volume or pressure variation occurring in each working space.
The power of the machine can be increased by increasing the quantity of working medium present in the various working spaces of the machine.
2. Description of the Prior Art
In the hot-gas reciprocating machine which is known from U.S. Pat. No. 4,045,978, the control device consists of a rotor which is rotatable relative to the enveloping housing and which is coupled to a shaft of the machine, the rotor also being reciprocable in the axial direction under the influence of a pressure on one side corresponding to an instantaneous cycle pressure (for example, the minimum, the mean or the maximum cycle pressure) which periodically occurs in a working space, and the source pressure on the other side.
When the power of this hot-gas reciprocating machine is to be increased, working medium is initially fed, exclusively by rotation of the rotor, to each working space during each revolution of the crankshaft for the period in which the maximum cycle pressure occurs in the relevant working space. Thus, the highest pressure of the working medium increases, so that the supplied working medium participates directly in the expansion, without the machine first having to perform compression work on the supplied medium, which would cause an initial decrease of the torque. Subsequently, a gradual change-over takes place from supplying working medium at maximum cycle pressure to that at minimum cycle pressure because, due to on the one hand the increasing continuous pressure acting on the rotor, representing the instantaneous cycle pressure and due to the decreasing source pressure acting on the rotor on the other hand, the rotor gradually assumes an axial position so that all outlet ports of the housing come into open communication with the inlet port.
The known hot-gas reciprocating machine has some drawbacks. The high working medium pressures necessitate proper sealing of the rotor shaft relative to the housing in order to prevent leakage of working medium to the surroundings. The service life of a high-pressure seal between mutually rotating parts, however, is short.
The control mechanism must satisfy very severe requirements as regards dimensional accuray (for example, narrow ducts in the rotor in the correct position in view of the instant of feeding of working medium).
Because a slip-free coupling between the rotor and a shaft of the machine is required, there is little freedom of choice of the position in which the control device is arranged.